1. Technical Field of the Invention
The present invention relates to a radio access network (RAN) and to an operation control method for the same. In particular, the present invention relates to an improvement of a radio network controller (RNC) in a W-CDMA (Wideband-Code Division Multiple Access) cellular system.
2. Description of the Related Art
FIG. 1 is a block diagram showing the structure of a mobile communication system including a conventional radio access network, i.e., a W-CDMA communication system.
As shown in FIG. 1, a radio access network (RAN) 1 comprises radio network controllers (RNCs) 4, 5 and node B's 6 to 9. The RAN 1 is connected to a mobile equipment (ME) 2 via a Uu interface (radio interface) and to a core network (CN) 3 via an Iu interface, where the CN 3 is an exchanger network providing a circuit exchanging service or packet exchanging service. The interface between one of node Bs 6 to 9 and one of RNCs 4, 5 is called Iub, and the interface between RNCs 4 and 5 is specified by Iur interface. The detail of the system shown in FIG. 1 is defined in 3GPP (Third Generation Partnership Projects) (for example, in 3GPP TS 25.401 V5.4.0 (2002-09), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Overall Description (Release 5)”).
Each of node B's 6-9 means a logical node of carrying out the radio transmission/reception, and more specifically it is a radio network device. Each node B 6-9 covers one or more cells 10, and it is connected to the mobile equipment (ME) 2 via the radio interface Uu, so that the radio link ends thereat.
An RNC is capable of controlling a plurality of radio networks, and serves managing the radio resources as well as controlling the hand-over. More specifically, RNC 4 and 5 perform the management of node B's 6-9 and the selection/synthesis of a radio path in the case of a soft hand-over. The structural arrangement of the RNC is formed in a unit by physically combining a function for controlling C (Control) plane as a protocol for signaling in the transmission of a control signal with a function for controlling U (User) plane as a protocol for transmitting user's data regarding the mobile equipment (ME) 2.
A signal is exchanged between ME 2 and CN 3 via the C (control) plane of the protocol for signaling in the transmission control of the control signal and the U (User) plane of the protocol for transmission control of the user's data. In this case, the C plane control function and the U plane control function, except the physical layer (PHY), are physically realized on an RNC.
In such a radio access network including the conventional RNC in which the C plane control function and the U plane control function are unified, it is necessary to include RNC itself in order to enhance the process rate for signaling, although, in this case, it is normally sufficient to add only the C plane control function thereto. Moreover, it is necessary to include RNC itself in order to enhance the transmission rate of user's data, although, in this case, it is normally sufficient to add only the U plane control function thereto. Accordingly, it is difficult to provide a system having both an excellent scalability and flexibility in the conventional RNC.
In view of these facts, an approach to separate the C plane control function from the U plane control function in the RAN has been made, so that it is proposed that a C plane control device for controlling the C plane and a U plane control device for controlling the U plane are physically separated from each other and disposed as independent units. In this structural arrangement, it is sufficient to additionally include only the C plane control device when the process ability for signaling is enhanced, and it is sufficient to additionally include only the U plane control device, when aiming to enhance the rate for transmitting the user's data. Thereby, a system having a satisfactory scalability can be realized. In an actual system, various arrangements are conceivable, for example, it is possible to assign n U plane control devices to a C plane control device, or to assign m U plane control devices to n C plane control devices. Moreover, in the case when m U plane control devices is assigned to n C plane control devices, it is possible to subordinate more than two C plane control device to a U plane control device.
For instance, in Japanese Patent Application No. 2002-185417, the present inventors have proposed a method for providing C plane information to ME, using a radio bearer controlled by a U plane control device, wherein a C plane control device for controlling the C plane is physically separated from the U plane control device for controlling the U plane, and a logical connection is interposed between the C plane control device and the U plane control device. This application is not yet published at present.
When, however, a C plane control device is physically separated from a U plane control device in a radio access network, the exchange of control information between protocol entities, which is closed so far inside the RNC, is carried out between various devices, so that the exchange of control information takes a lot of time and a complicate control system is further required to exchange the control information. For instance, when an ME is in the soft hand-over state, the setup of a new radio linkage and the release of the connected radio linkage cannot be carried out quickly, thereby causing the user's communication to be interrupted in an increased possibility.